This invention relates to coal particle suspensions and more particularly to a process for preparing a stabilized coal-water slurry.
While coal is a high density energy material comparable to other premium fossil fuels, it is more difficult to handle and transport in an efficient manner as compared to liquid or gaseous fuels. To alleviate the difficulties in handling and transporting coal, coal in particle form can be suspended in water to form a mobile, pumpable slurry.
In order to economically utilize a coal-water slurry for the transporting of coal, a stable and uniform suspension of coal particles at a relatively high concentration is necessary. To this end, numerous and various methods have been proposed to prevent or reduce the settling of coal particles in the slurry and maintain the desired suspension. One general approach has been to provide an external treatment or additive to the slurry such as dispersion agents which range from natural and synthetic water soluble polymers to ionic and non-ionic surfactants.
For example, U.S. Pat. No. 4,242,098 to Braun et al. utilizes water-soluble polymers and known dispersing aids including natural and synthetic gums and the like in the aqueous coal slurry to enhance the suspension of coal in the coal-water slurry. In U.S. Pat. No. 4,217,109 to Siwersson et al., polyelectrolytes and salts of polycarboxylic acid are utilized as dispersing agents in a coal-water slurry. European Pat. No. 0041337 to Allied Colloids Limited utilizes a synthetic polymeric dispersion agent made by polymerization of ethylenically unsaturated monomers such as acrylates, methacrylates, acrylamides or methacrylamides. Still another type of coal-water suspension aid is found in U.S. Pat. No. 4,261,701 to Schultz et al. which teaches the use of reaction products obtained from the oxidation of coal with bases or basic salts.
Another general approach has been to hinder the settling velocity of the coal particles by controlling the particle size distributions and coal specific gravities. An example of such an approach is the grinding of coal to practically colloidal size so that the smallness of size inherently reduces sedimentation as disclosed in U.S. Pat. No. 4,130,401 to Meyer et al. Also, in U.S. Pat. No. 4,132,365 to Verschuur, a controlled distribution of two or more classes of particle sizes with different specific gravities is utilized to improve stability.
However, both general approaches to improving stability pose significant disadvantages. The use of special dispersion agents is often prohibitively expensive and economically unacceptable. Furthermore, these agents often complicate their application because they require additional equipment or process designs in order to meet stringent environmental requirements. Therefore, the use of extraneous additives to improve the stability of coal-water slurries has attendant disadvantages.
Controlling the particle size distribution in order to improve stability also has significant disadvantages. For example, reducing the coal to practically colloidal size as disclosed in U.S. Pat. No. 4,130,401 is cost prohibitive because of the extensive milling required to reduce the particle size to that level. In addition to the considerable energy consumption required to accomplish the necessary size reduction, disadvantages in subsequent recovery of the colloidal size particles from the slurry may be encountered.
Therefore, it is desirable to attain a stable coal-water slurry without the addition of extraneous dispersion agents and additives and without extensive grinding and milling of the coal particles.
Accordingly, it is an object of this invention to provide a process for preparing a stablized coal particle suspension by utilizing the indigenous constituents that occur naturally in the coal.
It is also an object of the invention to provide a process for preparing a stabilized coal particle suspension without extraneous additives and dispersion agents and without extensive grinding and milling.
A further object of the invention is to provide a process for preparing a coal particle suspension that exhibits improved stability for ease of handling and transporting.
A still further object of the invention is to provide an economical and cost-efficient process for preparing a stabilized coal-water slurry.